A Compact Slow-Wave Filter with Double-sided Selectivity and Wide Out-of-Band Rejection

In this paper, a miniaturized filter with double-sided selectivity and wide out-of-band rejection is presented. The slow-wave and negative cross-coupling structures are effectively adopted to realize an ultra-compact K-band filter with two symmetric transmission zeros. Starting from a bandpass filter configured for a center frequency of 18.5 GHz and the main-line couplings that only exhibits a good out-of-band rejection of 30 dB up to 30 GHz, the two proposed negative cross-couplings enable the steep roll-off out-of-band rejections as well as low in-band insertion losses of 1.7 dB and 2.4 dB. The designed structures are utilizing both the additive manufacturing and PCB-based technology which in turn, provide a simple, low-profile, and cost-effective fabrication process for highly integrated RF systems, particularly in satellite applications.